Conquest File System

The rapidly declining cost of persistent RAM technologies prompts
the
question of when, not whether, such memory will become the preferred
storage
medium for many computers. In anticipation of that development,
we
present Conquest, a file system that provides a transition from
disk to persistent RAM as the primary storage medium. Conquest
is
incrementally deployable and realizes most of the benefits of
persistent
RAM as it becomes cheaply abundant. As of October 2001, Conquest
can be used effectively for a hardware cost of below $200.

We compare Conquest's performance to ext2, reiserfs,
SGI XFS,
and ramfs, using popular benchmarks. Our measurements
show
that Conquest incurs little overhead compared to ramfs.
Compared to disk-based file systems, Conquest achieves 24% to
1900%
faster performance for working sets that fit in memory, and 43% to 96%
faster performance with working sets larger than the memory size.

Conquest Architecture

Conquest uses memory to store all metadata, small files
(currently
based on a size threshold), executables, and shared libraries, leaving
only the content of large files on disk. All accesses to in-core
data and metadata incur no data duplication or disk-related overhead,
and
executions are in-place. For the large-file-only disk storage, we
use a larger access granularity to reduce the seek-time overhead.
Because most accesses to large files are sequential, we can relax many
historical disk design constraints, such as complex layout heuristics
intended
to reduce fragmentation or average seek times.